This invention relates to electromechanical systems, and more particularly to microelectromechanical systems and operating methods therefor.
Microelectromechanical systems (MEMS) have been developed as alternatives to conventional electromechanical devices, such as relays, actuators, valves and sensors. MEMS devices are potentially low-cost devices, due to the use of microelectronic fabrication techniques. New functionality also may be provided, because MEMS devices can be much smaller than conventional electromechanical devices.
Many applications of MEMS technology use MEMS actuators. These actuators may use one or more beams that are fixed at one or both ends. These actuators may be actuated electrostatically, magnetically, thermally and/or using other forms of energy.
A major breakthrough in MEMS actuators is described in U.S. Pat. No. 5,909,078 entitled Thermal Arched Beam Microelectromechanical Actuators to the present inventor et al., the disclosure of which is hereby incorporated herein by reference. Disclosed is a family of thermal arched beam microelectromechanical actuators that include an arched beam which extends between spaced apart supports on a microelectronic substrate. The arched beam expands upon application of heat thereto. Means are provided for applying heat to the arched beam to cause further arching of the beam as a result of thermal expansion thereof, to thereby cause displacement of the arched beam.
Unexpectedly, when used as a microelectromechanical actuator, thermal expansion of the arched beam can create relatively large displacement and relatively large forces while consuming reasonable power. A coupler can be used to mechanically couple multiple arched beams. At least one compensating arched beam also can be included which is arched in a second direction opposite to the multiple arched beams and also is mechanically coupled to the coupler. The compensating arched beams can compensate for ambient temperature or other effects to allow for self-compensating actuators and sensors. Thermal arched beams can be used to provide actuators, relays, sensors, microvalves and other MEMS devices. Thermal arched beam microelectromechanical devices and associated fabrication methods also are described in U.S. Pat. No. 5,955,817 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Switching Array; U.S. Pat. No. 5,962,949 to Dhuler et al. entitled Microelectromechanical Positioning Apparatus; U.S. Pat. No. 5,994,816 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Devices and Associated Fabrication Methods; and U.S. Pat. No. 6,023,121 to Dhuler et al. entitled Thermal Arched Beam Microelectromechanical Structure, the disclosures of all of which are hereby incorporated herein by reference in their entirety.
Unfortunately, conventional MEMS actuators may require continuous application of an electrostatic potential, a magnetic field, electric current and/or other energy to the MEMS actuator in order to maintain the actuator in a set or actuated position. This may consume excessive power. Moreover, an interruption of power may cause the actuator to reset.
It is known to provide notches, dimples, protrusions, indentations and/or other mechanical features in MEMS actuators that can allow the actuator to be mechanically set in a given position. See for example, the above-cited U.S. Pat. Nos. 5,955,817 and 5,994,816. Unfortunately, these mechanical features may be subject to wear. Moreover, mechanical locking that relies on friction may be difficult to obtain reliably due to the small dimensions of MEMS actuators and the uncertain values of static and dynamic friction in MEMS devices. Thus, notwithstanding conventional microelectromechanical devices, there continues to be a need for lockable microelectromechanical actuators that need not consume power when locked and need not rely on mechanical friction for locking.
Lockable microelectromechanical actuators according to embodiments of the invention include a microelectromechanical actuator, a thermoplastic material that is coupled to the microelectromechanical actuator to lock the microelectromechanical actuator, and a heater that melts the thermoplastic material to allow movement of the microelectromechanical actuator. When the thermoplastic material solidifies, movement of the microelectromechanical actuator can be locked, without the need to maintain power, in the form of electric, magnetic and/or electrostatic energy, to the microelectromechanical actuator, and without the need to rely on mechanical friction to hold the microelectromechanical actuator in place. Thus, the thermoplastic material can act as a glue to hold structures in a particular position without the need for continuous power application. Moreover, it has been found unexpectedly, that the thermoplastic material can solidify rapidly enough to lock the microelectromechanical actuator at or near its most recent position.
Embodiments of the present invention preferably are formed on a substrate, wherein the heater is on the substrate and wherein a portion of the microelectromechanical actuator is adjacent and spaced apart from the heater, and wherein the thermoplastic material is between the heater and the portion of the microelectromechanical actuator. The microelectromechanical actuators may move along the substrate to provide embodiments of xe2x80x9cin-planexe2x80x9d microelectromechanical actuators. Alternatively, the actuators may move out of the plane of the substrate, for example, orthogonal to the substrate, to provide embodiments of xe2x80x9cout-of-planexe2x80x9d microelectromechanical actuators.
Embodiments of the present invention may be used with actuators that are actuated using electrostatic, magnetic, thermal and/or other forms of actuation. In embodiments of thermally actuated microelectromechanical actuators, the heater that melts the thermoplastic material also may be used to actuate the thermally actuated microelectromechanical actuator. In alternative embodiments, the heater that melts the thermoplastic material is a first heater and the lockable microelectromechanical actuator also includes a second heater that is thermally coupled to the microelectromechanical actuator, such that the microelectromechanical actuator moves in response to actuation of the second heater. Embodiments of lockable microelectromechanical actuators that employ first and second heaters also may include a thermal isolator that is configured to isolate the second heater from the thermoplastic material.
In embodiments of the present invention that use the same heater to melt the thermoplastic material and to actuate the thermal actuator, the heater may be configured to melt the thermoplastic material and actuate the thermal actuator upon application of a first amount of power thereto. The heater also may be configured to melt the thermoplastic material without actuating the thermal actuator upon application of second amount of power thereto that is less than the first amount of power. Unexpectedly, it has been found that the actuator can be restored to its starting or unactuated position by applying sufficient power to the heater to melt the thermoplastic material, but not enough power to actuate the actuator. With the thermoplastic material melted, viscous flow can occur and permit the actuator to relax back to its neutral position. Thus, a reversible system may be provided, that can allow continuous variability and simple control setup.
Thermoplastic materials according to the present invention may include thermoplastic polymers, thermoplastic monomers, solders and/or any other material that changes from a solid to a liquid material over a temperature range that is compatible with the ambient temperature in which the lockable microelectromechanical actuator will be used. Embodiments of lockable microelectromechanical actuators according to the invention may be combined with a relay contact, an optical attenuator, an optical switch, a variable circuit element such as a variable resistor, a valve, a circuit breaker and/or other elements to provide a microelectromechanical device.
Other embodiments of the invention provide lockable thermal arched beam microelectromechanical actuators. Embodiments of thermal arched beam microelectromechanical actuators include a substrate, spaced apart supports on the substrate and an arched beam that extends between the spaced apart supports, and that further arches upon application of heat thereto for movement along the substrate. A thermoplastic material is coupled to the arched beam to lock the arched beam. A heater melts the thermoplastic material to allow movement of the arched beam. In preferred embodiments, the heater is on the substrate, the arched beam is adjacent and spaced apart from the heater, and the thermoplastic material is between the heater and the arched beam.
Embodiments of lockable thermal arched beam microelectromechanical actuators use the heater both to further arch the arched beam and to melt the thermoplastic material. Alternative embodiments use a first heater to melt the thermoplastic material and a second heater that is thermally coupled to the arched beam to further arch the arched beam. These alternative embodiments also may include a thermal isolator that is configured to thermally isolate the second heater from the thermoplastic material.
As was described above, in embodiments of lockable thermal arched microelectromechanical actuators wherein a single heater is used, the heater may be configured to melt the thermoplastic material and to further arch the arched beam upon application of a first amount of power thereto. The heater also may be configured to melt the thermoplastic material without further arching the arched beam upon application of a second amount of power thereto that is less than the first amount of power. Embodiments of lockable thermal arched beam microelectromechanical actuators can use the thermoplastic materials selected that were described above, and can be combined with other elements as was described above.
Other embodiments of lockable thermal arched beam microelectromechanical actuators use first and second parallel arched beams that further arch upon application of heat thereto. A coupler is attached to the first and second arched beams, such that the first and second arched beams move in tandem along the substrate upon application of heat thereto. In these embodiments, the thermoplastic material may extend between the coupler and the heater. The coupler may include an aperture that extends therethrough from opposite the heater to adjacent the heater and that is configured to allow placement of the thermoplastic material between the coupler and the heater.
Microelectromechanical actuators may be operated, according to embodiments of the present invention, by melting a thermoplastic material that is coupled to the microelectromechanical actuator to unlock the microelectromechanical actuator. The unlocked microelectromechanical actuator may be actuated. The melted thermoplastic material then may be allowed to solidify to lock the microelectromechanical actuator. In embodiments of these methods, the melting and actuating may be performed simultaneously. In other embodiments, melting of the thermoplastic material is performed by applying power to a heater that is thermally coupled to the thermoplastic material. The melted material is solidified by removing the power from the heater.
In alternative embodiments of methods according to the present invention, the microelectromechanical actuator is a thermally actuated microelectromechanical actuator wherein the heater also is thermally coupled to the thermally actuated microelectromechanical actuator. Power is applied to the heater to actuate the thermally actuated microelectromechanical actuator. Melting and actuating may be performed simultaneously by applying power to the heater.
In alternate embodiments of methods according to the present invention wherein the microelectromechanical actuator includes a first heater that is thermally coupled to the thermoplastic material and includes a second heater that is thermally coupled to the thermally actuated microelectromechanical actuator, melting may be performed by applying power to the first heater to melt the thermoplastic material. Actuating may be performed by applying power to the second heater, to actuate the thermally actuated microelectromechanical actuator. Power then may be removed from the heater, to allow the melted thermoplastic material to solidify.
In all of the above method embodiments, the step of allowing the melted thermoplastic material to solidify may be followed by again melting the thermoplastic material to again unlock the microelectromechanical actuator. The microelectromechanical actuator then can return to its neutral or retracted position. Thus, by melting the thermoplastic material, the microelectromechanical actuator can be unlocked and deactuated.
In embodiments of the present invention wherein a single heater also is used to thermally actuate the microelectromechanical actuator, the step of again melting the thermoplastic material may be performed by applying power to the heater that is sufficient to melt the thermoplastic material, but is insufficient to actuate the thermally actuated microelectromechanical actuator. The actuator thereby can deactuate or retract. In alternative embodiments wherein first and second heaters are used as described above, the step of again melting the thermoplastic material may be embodied by applying power to the first heater to melt the thermoplastic material without applying power to the second heater.
Accordingly, lockable microelectromechanical actuators including lockable thermal arched beam microelectromechanical actuators, may be provided. These actuators need not consume power to remain actuated and need not rely on mechanical friction to maintain actuation. Thermoplastic materials also may be used to produce lockable large scale actuators that are not microelectromechanical actuators.